题意：
给出一个表达式..包含'+' '-' '*' '/' '.' 以及空格..
求出表达式的值..
思路：
栈的应用..
Tips：
①. 指针引用那里..参数是字符串首地址不可以改变..
而如果是指针..就可以改变..所以把字符串首地址作为参数传给change函数不可以..但是先传给函数calculate变成了指针再传给change就可以arr++了..
②. 运算符优先级可以用一个二维数组来判断..
Code：
View Code
1 #include <stdio.h> 2 #include <cstring> 3 #include <iostream> 4 #include <algorithm> 5 #include <ctype.h> 6 #include <map> 7 using namespace std; 8 9 struct Node 10 { 11 char arr[1024]; 12 int st; 13 int en; 14 }node[1024]; 15 16 const int MAXN = 40; 17 int com[250][250]; 18 19 void ini() 20 { 21 memset(com, 0xff, sizeof(com)); 22 com['+']['+'] = com['+']['-'] = com['+'][')'] = com['+']['#'] = 1; 23 com['-']['-'] = com['-']['+'] = com['-'][')'] = com['-']['#'] = 1; 24 com['*']['+'] = com['*']['-'] = com['*']['*'] = com['*']['/'] = com['*'][')'] = com['*']['#'] = 1; 25 com['/']['+'] = com['/']['-'] = com['/']['*'] = com['/']['/'] = com['/'][')'] = com['/']['#'] = 1; 26 com[')']['+'] = com[')']['-'] = com[')']['*'] = com[')']['/'] = com[')'][')'] = com[')']['#'] = 1; 27 com['('][')'] = com['#']['#'] = 0; 28 } 29 30 double change(char *&arr) 31 { 32 double sum = 0; 33 bool flag = false; 34 int d = 0; 35 while(isdigit(*arr) || *arr == '.') { 36 if(*arr != '.') sum = sum * 10 + (*arr-'0'); 37 if(flag) d++; 38 if(*arr == '.') 39 flag = true; 40 arr++; 41 } 42 if(flag) 43 while(d--) { 44 sum *= 0.1; 45 } 46 return sum; 47 } 48 49 double cal(double a, char o, double b) 50 { 51 if(o == '+') return a+b; 52 else if(o == '-') return a-b; 53 else if(o == '*') return a*b; 54 else if(o == '/') return a/b; 55 } 56 57 bool isoptr(char c) { 58 if(c == '(' || c == '+' || c == '-' || c == '*' || c == '/' || c == ')' || c == '#') return true; 59 else return false; 60 } 61 62 double calculate(char *arr) 63 { 64 char optr[MAXN]; 65 double opnd[MAXN]; 66 char c; 67 double a, b; 68 int top1 = 0, top2 = 0; 69 optr[top1++] = '#'; 70 while(*arr != '#' || optr[top1-1] != '#') { 71 if(*arr == ' ') 72 arr++; 73 else if(!isoptr(*arr)) { 74 opnd[top2++] = change(arr); 75 } else { 76 c = optr[top1-1]; 77 switch(com[c][*arr]) { 78 case -1: 79 optr[top1++] = *arr; 80 arr++; 81 break; 82 case 0: 83 --top1; 84 arr++; 85 break; 86 case 1: 87 c = optr[--top1]; 88 b = opnd[--top2]; 89 a = opnd[--top2]; 90 opnd[top2++] = cal(a, c, b); 91 break; 92 } 93 } 94 } 95 return opnd[top2-1]; 96 } 97 98 int main() 99 { 100 char arr[1024]; 101 ini(); 102 while(gets(arr)) { 103 int len = strlen(arr); 104 // printf("%s\n", arr); 105 arr[len] = '#'; 106 printf("%.2lf\n", calculate(arr)); 107 } 108 109 }
题目链接：http://acm.hrbust.edu.cn/index.php?m=ProblemSet&a=showProblem&problem_id=1572